A motor-driven vehicle, e.g. a motor-driven wheelchair, has a pair of drive wheels which are driven by motors. A control apparatus controls the respective motors.
An example of control apparatus for use with a motor-driven wheelchair is shown in EP 0 691 232 A2 published on Jan. 10, 1996 which is incorporated hereinto by reference. The motor-driven wheelchair with the motor control apparatus shown in this European publication includes manual-driving-force sensing units which sense the magnitudes of forces applied to the wheelchair to move it by an attendant to a user of the wheelchair. The manual-driving-force sensing units produce manual-driving-force representative signals which are proportional to the magnitudes of the manual driving forces applied to the wheelchair. The manual-driving-force representative signals are applied to the control apparatus, which controls the motors in such a manner as to produce wheel driving forces proportional to the corresponding manual-driving-force representative signals.
As the manual driving forces applied to the wheelchair increase, the wheel driving forces developed by the respective motors increase proportionally. Accordingly, when the running resistance of the wheelchair increases, e.g. when the wheelchair moving on a flat path must go up a slope, so that the wheel driving forces of the motors must be increased, the manual driving forces must be increased, too. That is too burdensome to an attendant having small strength.
With the control apparatus shown in the above-quoted European publication, changes of manual driving forces immediately cause changes of the wheel driving forces of the motors. Accordingly, if, for example, the manual driving forces for driving the wheelchair in the forward direction are increased, which results in acceleration at a high rate of the wheelchair, the attendant may not be able to follow the movement of the wheelchair. Then, he or she will try to reduce the manual driving forces, or, in some cases, may apply to the wheelchair manual driving forces to cause the wheelchair to move in the opposite, i.e. backward direction. In such a case, the wheel driving forces developed by the motors may abruptly decrease, or the motors may develop wheel driving forces which tend to drive the wheels in the backward direction. In response to such changes of the wheel driving forces of the motors, the attendant may increase his or her manual driving forces to drive the wheelchair in the forward direction. As a result, the wheelchair is accelerated in the forward direction at a high rate, again. In this way, the wheelchair is alternately accelerated and decelerated. In other words, the moving speed of the wheelchair is unstable. Accordingly, in order to drive the wheelchair at a stable speed, the attendant needs to have skill in driving the wheelchair.
An object of the present invention is to provide a control apparatus for use with a motor-driven vehicle which can make motors of the motor-driven vehicle increase their driving forces, without increasing burden on a vehicle operator. Hereinafter, driving force provided by a motor is referred to as supplementary, mechanical driving force, or supplementary driving force, or mechanical driving force.
Another object of the present invention is to provide a motor control apparatus for use with a motor-driven vehicle which can make the supplementary, mechanical driving forces change smoothly even if manual driving forces applied to the vehicle changes abruptly.